ktk.write_c3d generates an error if file doesn't end by .c3d

[felixchenier]

Initially discussed in #229

Describe the bug

import kineticstoolkit as ktk
ts = ktk.read_c3d("data/kinematics_racing_full.c3d")
ktk.write_c3d("test_file", points=ts["Points"])

generates a correct file, but with this error message.

File "~/miniconda3/envs/ktk_env/lib/python3.12/site-packages/ezc3d/ezc3d.py", line 1874, in __init__
    _ezc3d.c3d_swiginit(self, _ezc3d.new_c3d(*args))
                              ^^^^^^^^^^^^^^^^^^^^^
RuntimeError: Could not open the c3d file: unspecified iostream_category error

Python version
3.12

Waiting for @Alek050 to know this information:

Python installation
Select: python.org, Anaconda, conda-forge, etc.

Operating system

• OS: [e.g. macOS, Windows, Linux]
• Version [e.g. Big Sur, 10]

[Alek050]

Hi @felixchenier ,

Thanks for looking into this. As a matter of fact, I am on MacOs (Sonoma 14.2, with M1 chip). I looked into the ezc3d issue you referred to, but since I am on mac the UTF-8 encoding should not be a problem. Furhtermore, you can see I am saving a file called test_file, which does not have any accents or spaces in it.

Some environment info:

• Python version: 3.12.2
• Python installation: conda-forge
• Operating system: MacOs 14.2
• ezc3d version: 1.5.9 (conda-forge)
• kineticstoolkit version: the VERSION file states 0.13.master, but I am up to date with the current master branch which should be 0.14 I think.

For sake of completeness here:
Interstingly, I do not get an error when using the example provided by ezc3d:

import numpy as np

import ezc3d

# Load an empty c3d structure
c3d = ezc3d.c3d()

# Adjust some mandatory values of the parameters and fill the data with random values
c3d["parameters"]["POINT"]["RATE"]["value"] = [100]
c3d["parameters"]["POINT"]["LABELS"]["value"] = ("point1", "point2", "point3", "point4", "point5")
c3d["data"]["points"] = np.random.rand(3, 5, 100)

c3d["parameters"]["ANALOG"]["RATE"]["value"] = [1000]
c3d["parameters"]["ANALOG"]["LABELS"]["value"] = ("analog1", "analog2", "analog3", "analog4", "analog5", "analog6")
c3d["data"]["analogs"] = np.random.rand(1, 6, 1000)

# Create a custom parameter to the POINT group
c3d.add_parameter("POINT", "NewParam", [1, 2, 3])

# Create a custom parameter a new group
c3d.add_parameter("NewGroup", "NewParam", ["MyParam1", "MyParam2"])

# Write a new modified C3D and read back the data
c3d.write("temporary.c3d")

Similarly, the example of ktk also seems to work (even when reading in only the analogs data):

import kineticstoolkit.lab as ktk
import numpy as np

points = ktk.TimeSeries()
points.time = np.linspace(0, 10, 10*240, endpoint=False)
points.data["Marker1"] = np.ones((2400, 4))
points.data["Marker2"] = np.ones((2400, 4))

analogs = ktk.TimeSeries()
analogs.time = np.linspace(0, 10, 10*2400, endpoint=False)
analogs.data["Signal1"] = np.sin(analogs.time)
analogs.data["Signal2"] = np.cos(analogs.time)

rotations = ktk.TimeSeries()
rotations.time = np.linspace(0, 10, 10*480, endpoint=False)
rotations.data["Rotation1"] = np.ones((4800, 4, 4))
rotations.data["Rotation2"] = np.ones((4800, 4, 4))

ktk.write_c3d("testfile.c3d", rotations=rotations)
ktk.write_c3d("testfile.c3d", points=points)
ktk.write_c3d("testfile.c3d", analogs=analogs)
ktk.write_c3d("testfile.c3d", points=points, analogs=analogs, rotations=rotations)

I am not really sure why it does not work since type(ts["Points"]) and type(points)) both give are <class 'kineticstoolkit.timeseries.TimeSeries'>. (ts as defined in the first code block of the comment of @felixchenier and points as defined in my comment above in the last code block)

[felixchenier]

As an additional information, I am quite sure this is generated not when writing the C3D, but when we read it again to add the events, something that has been done as a workaround for pyomeca/ezc3d#263

This has not been reproduced by @pariterre and I forgot about it. I'll revisit it when I'll investigate this issue more deeply.

[felixchenier]

Hi @Alek050

OK I think I got it :-)

In your original bug description:

import kineticstoolkit as ktk
ts = ktk.read_c3d("data/kinematics_racing_full.c3d")
ktk.write_c3d("test_file", points=ts["Points"])

You didn't put ".c3d" in the file name. If you do, it's ok.

Let's simply add

    if not filename.lower().endswith(".c3d"):
        raise ValueError("filename must end with .c3d")

just after the first check_param calls.

[Alek050]

Works as a charm, sorry for the inconvenience, will add it in the pull request as well.

[felixchenier]

Done in branch PR232